Differential air gauge



June 9, 1953 G. w. GRlsDALE DIFFERENTIAL AIR GAUGE Filed April 16, 1947 INVENTUR. VV. ERISDALE.

.EEDREE Patented June 9, 1953 UNITED STATES PATENT OFFICE (Granted under Title 35, U. S. lCode (1952),

sec. 266) 3 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to gages which operate by the dilierential pressure of air passing through them. Such gages are particularly adapted for measuring in response to the variations in the gap between the outlet member of the gage and a work piece, such as the interior of a gun barrel. However, such gages may be employed for indicating any differential fluid pressure.

One object of the present invention is to provide a gage having an orifice Oi' fixed size across which orifice pressure differential is measured and at the same time having part of the indicating element of the gage passing through the orice.

Another object of the invention is to improve the quality and character of gages.

Further objects of this invention are to provide a simple and accurate iiuid pressure operated gage which can be easily and economically manufactured and which is eiiicient and exact in use since it is easily read.

The invention also comprises the improvements to be presently described and finally claimed.

In the following description reference will be made to the accompanying drawing forming part hereof and in which:

Fig. 1 is a top or plan view with parts broken away in horizontal cross section.

Fig. 2 is a front elevation with parts broken away in vertical cross section to reveal the internal structure.

In the drawings, the gage of this invention will be seen to consist of a housing or casing made in two parts of which the upper is designated by the reference character 5 and the lower by the reference character 6. This housing or casing is supported on a base 1. The upper part 5 of the housing has in inlet I9 communicating with a high pressure chamber 40 whose opposite or outlet end communicates with an oriiice I passing through a slab or plate I I. Slab or plate I I may be readily removed from the housing and replaced with another having an orifice of diierent size through it. The upper part of the housing is generally arcuate in vertical cross section and has a correspondingly shaped window cr opening I2. The upper and lower arcuate edges oi window I2 are channeled or grooved to receive the edges of a maximum clearance indicator I4 and a minimum clearance indicator I5 whereby these indicators are mounted for manual adjustment in a manner obvious from inspection of the drawing. These indicators are in the form of sheets or plates cut away at one side to provide indexes I6 and I1 respectively. The rear or inner face of window I2 is closed and sealed by a transparent pane I8. The lower housing part 6 forms a generally arcuate low pressure chamber 9 having an exhaust or outlet connection 8.

Bearing members 2liK and 24 are mounted in aligned relation in the upper central portion of the walls of lower housing G and have axially aligned bores in their confronting ends to receive the reduced ends or spindles 2l and 23 respectively, of shaft 22 to provide an anti-friction pivotal mounting for the same. Member 20 is threaded into a tapped hole in one wall of the housing, while member 24 is threaded into a sleeve 25 having a smooth iit within an enlarged bore in the other wall of the housing. This sleeve has an inner flange which is drawn against a shoulder in the inner face of said other wall by means of a nut 2E upon a reduced threaded exterior portion, whereby the sleeve is rigidly secured to the housing. The inner end of sleeve 25 is reduced and an upstanding support 21 has a press fit thereon. This support bears an inwardly projecting pin 28 on its distal end to which is ailxed the outer end of a coil spring 29. The other end of spring 29 is secured to shaft or spindle 22.

Also mounted on spindle 22 is an indicator 3D in the form of a flat plate having a pointer 3l visible through pane. I8, and oppositely extending stops 32 and 320 formed in its upper portion. A rearwardly extending flange 33 is turnedvback out of its plane and has a perforation through which passes a portion of a piston 34.

Piston 34 is in the form of a length of stiff wire in arcuate form and fixed to pointer 3I coaxially of shaft 22 by loop formed on one end of the wire in cooperation with a rivet 36 and also by the aforesaid iiange 33.

Communicating with outlet orifice 8 is a flexible tube 31 on the opposite end of which is mounted a measuring piston 38 having one or more oriiices 39 in its side walls and in communication with the contiguous end of tube 31. The measur ing piston 38 is adapted for insertion into the work piece to be measured such as the gun barrel W indicated in dotted lines in Fig. 2.

. The method or mode of operation of the gage of this invention is as follows: The inlet I9 is connected to a suitable source of constant pressure fluid such as compressed air. The helically coiled spring 29 stresses or biases indicator 30 clockwise in the direction shown by the arrow A in Fig. 2. The right-hand stop 320 is therefore 3 in contact with the xed stop 50 (Fig. 2) when the device is at rest. When the compressed air is admitted to the inlet |9 it passes in the direction of the arrows B through high pressure charnber 40, the fixed orifice I0, the back pressure chamber 9, the outlet orifice 8, the tube 31, and out through the orifice or orifices 39. Since the only communication between the chambers in casing parts 5 and 6 is through restricted orifice I0, there is a pressure drop between chambers which acts upon the piston 34 to urge the same and pointer 3| counterclockwise, withv a torque proportional to the pressure difference or rate of flow of fluid through the orifice. If the measuring piston 38 is now inserted into the interior of the work piece which is to be gaged, such as the gun barrel W, the escape of air from the measuring orice 39 is reduced and consequently the pressure drop across and rate of iiow of uid.

through the orice decreases so that spring 29 moves indicator 39 as indicated by arrow A in a clockwise direction, or to the right as seen in Fig.

2, The amount of clockwise or right-hand movebetween the measuring piston 38 and the maximum and minimum setting rings, the pointer 3| occupies a different position when the minimum setting ring is over the measuring piston 38. This position of pointer 3| is observed and the minimum clearance indicator I5 is moved so that its pointed markers coincide with the axis of the pointer, Thus the maximum and minimum clearance indicators are set to provide tolerance or gage points between which the finger 3| should be located when the measuring piston 38 is inserted in the work piece W being gaged, in order to pass as satisfactory each of the work pieces being gaged. If the ringer 3| lies beyond the pointed markers I4 or I6 in either direction, the work piece is either too small or too large.

I claim:

1. In a differential pressure gage, a casing comu prising upper and lower halves having inlet and outlet connections, respectively, and generally horizontal confronting mating faces secured t0- gether t0 define first and second pressure chambers communicating only through an orice in the interface of one said half, aligned bearings carried by the opposed side walls of said lower half and defining a pivot axis radially offset from said orifice, a shaft journaled by and between said bearings for rotation about said axis, a pointer fixed with said shaft and viewable through a sealed viewing opening in said Lipper half, an arcuate piston secured at one end with said pointer and extending loosely through said orice coaxially of said axis, and a spring yieldingly urging said shaft in one direction of rotation.

2. In a differential pressure gage, a lower cas- 4 ing half having walls defining a closed rst pressure chamber, an upper casing half secured to and over said lower half and defining therewith a closed second pressure chamber, the wall of said lower half having an apertured flat surface between said chambers, a fiat plate removably secured to and over said surface and having an orifice superpcsed over the aperture therein, rst and second bearings mounted in aligned relation in respective side walls of said lower casing to define an axis radially offset from said orifice, a shaft journaled by and between said bearings, a pointer member radially secured to and upstanding from said shaft and Viewable through an arcuate sealed viewing opening in the wall of said upper half, an arcuate piston iixed to said pointer member coaxially of said shaft and extending loosely through said oriice throughout the range 4of angular movement of said shaft, spring means urging said shaft into one direction of rotation, and inlet and outlet connections in communication with said chambers.

3. In a differential pressure gage, a lower casing half having walls defining a closed rst pressurev chamber, an upper casing half secured to and over said lower casing half to define therewith a second closed pressure chamber, a plate replaceably secured over an aperture in the wall between said chambers and having an oricesuperposed over the aperture, there being aligned bearing openings in respective opposed walls of said lower casing half deiining an axis radially offset from the orifice, a first bearing threaded into one said opening, a sleeve secured in and tting the other said opening, a second bearing threadedly engaging said sleeve, a shaft journaled by and between said bearings for rotation on said axis, a pointer member secured to said shaft and viewable through a sealed opening in said upper casing half, an arcuate piston fixed to said pointer member coaxially of said shaft and extending loosely through said orifice, a support xed to the inner end of said sleeve and extending radially therefrom within said second chamber, a coil spring having one end secured to said support and the other end to said shaft, and outlet and inlet connections carried by the respective casing halves and in communication with the respective chambers.

GEORGE W. GRISDALE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,107,298 Haas Aug. 18, 1914 1,111,684 Vaughan Sept. 22, 1914 1,397,518 Hem Nov. 22, 1921 v1,401,887 Davis Dec. 27, 1921 1,788,976 Beraud et al Jan. 13, 1931 1,888,298 Teesdaie Nov. 22, 1932 1,927,750 Mennesson Sept. 19, 1933 2,254,259 Auer sept. 2,1941 2,262,807 Larner Nov. 18, 1941 2,350,058 May May 30, 1944 2,446,632 Cahill et al. Aug. 10, 1948 FOREIGN PATENTS Number Country Date 641,047 Germany Jan. 22, 1937 241,935 Switzerland Sept. 16, 1946 

